The file domains.txt contains a list of domain names, one per line, which contains companies that have acquired my contact details through Lusha, Zoominfo, Cognism, Seamless, Apollo, LeadIQ, Slintel, etc. They are an absolute annoyance, so I suggest you block does domain name at SMTP time on your email gateways.
One domain, per line, with a company that has opted me in without my consent.